Aldehydes and Ketones Flashcards
Why are the alpha-H of aldehydes and ketones acidic
Alpha-H of aldehydes and ketones are acidic, or deprotonate easily, due to both inductive effects and resonance effects. The electronegative oxygen atom pulls electron density from the C-H bond, weakening it. Once deprotonated, the resonance stabilization of the negative charge between the alpha-carbon, carbonyl carbon, and electron- withdrawing carbonyl oxygen increases the stability of this form.
Are the alpha H of aldehydes or ketone are more acidic and why?
The alpha- H of the aldehydes are slightly more acidic due to the electron donating characteristics of the second alkyl group in ketones. This extra alkyl group destabalizes the carbanion, which slightly disfavors the loss of the alpha- H in ketones as compared to aldehydes.
How does steric hindrance affect the relative reactivity of aldehydes and ketones
Steric hinderance is one of the two reasons that aldehyde are slightly more reactive than ketones. The additional alkyl group gets in the way and makes for higher-energy crowded intermediate
What are tautomers
Isomers that can be interconverted by movement of H and double bond
What tautomer of aldehyde and ketone is therodynamically favored?
Keto form is favored
What role does the enolate carbocation play in organic reactions: nucleophile, electrophile, oxidizing agent or reducing agent?
enolate carbocations act as nucleophile
What conditions favor kinetic control of products
Can form rapidly, irreversible, can interconvert with the thermo form if given enough time, with strong, sterically hindered base
What conditions favor thermodynamic control of products
Slower, reversible reactions, with weaker or smaller bases and higher temperature
What species acts as the nucleophile in an aldol condensation
enolate carbocation acts as the nucleophile (the deprotonated aldehyde or ketone)
What species acts as the electrophile in an aldol condensation
The keto form of the aldehyde or ketone acts as the nucleophile
What is a retro-aldol reaction? What conditions favor retro-aldol reactions?
The retro-aldol reaction is the reverse of a aldol reaction and can be favored by the addition of base and heat. In this reaction, a bond between the alpha and beta carbons of a carbonyl is broken forming 2 aldehydes and 2 ketones or one aldehyde and one ketone
What kind of reaction is aldol reaction
Condensation
dehydration
Nucleophile-electrophile
